Conventionally, refrigeration cycle apparatuses in which a chlorofluorocarbon or an alternative chlorofluorocarbon is used as a refrigerant are widely used. However, such refrigerants are responsible for the problems such as ozone depletion and global warming. In view of this, refrigeration cycle apparatuses have been proposed in which water is used as a refrigerant that places only an extremely small load on the global environment. As an example of such a refrigeration cycle apparatus, Patent Literature 1 discloses an air conditioner specialized for cooling.
When water is used as a refrigerant, a large amount of refrigerant vapor needs to be compressed at a high compression ratio. Accordingly, the air conditioner disclosed in Patent Literature 1 uses two compressors, i.e., a centrifugal compressor and a positive-displacement compressor, and the compressors are arranged in series so that a refrigerant vapor compressed by the centrifugal compressor is further compressed by the positive-displacement compressor.
In addition, when water is used as a refrigerant, the temperature of the refrigerant discharged from a compressor is high due to the physical properties of water. Therefore, the durability of members constituting a high-pressure part of the air conditioner is reduced. In order to address this problem, it is effective to dispose an intercooler between the upstream-side compressor and the downstream-side compressor as in the air conditioner disclosed in Patent Literature 1, and thus to temporarily reduce the temperature of the refrigerant vapor in the course of compression process.